Encapsulation process

ABSTRACT

A protective colloid for use in an interfacial polymerization process comprising a graft copolymer of polyvinyl alcohol and methyl vinyl ether/maleic acid.

This is a divisional of application Ser. No. 383,448, filed June 1,1982.

FIELD OF THE INVENTION

This invention relates to an interfacial polymerization process and, inparticular, to an improved protective colloid for use in such a process.

BACKGROUND OF THE INVENTION

The use of membranes, coatings and capsules for the controlled releaseof liquid materials is well known in the art of both agricultural andnon-agricultural chemicals. In agriculture, controlled releasetechniques have improved the efficiency of herbicides, insecticides,fungicides, bactericides, and fertilizers. Non-agricultural uses includeencapsulated dyes, inks, pharmaceuticals, flavoring agents, andfragrances.

The most common forms of controlled-release materials are coateddroplets or microcapsules, coated solids including both porous andnon-porous particles, and coated aggregates of solid particles. In someinstances, the coating is porous and the entrapped material is releasedto the surrounding medium at a slow rate by diffusion through the pores.In other instances, the encapsulating film is water-soluble and theencapsulated material is released when the capsule is placed in contactwith water. Still other coatings release the entrapped material when thecoating is ruptured by external force.

This invention relates to porous coatings. In addition to providingcontrolled release, these coatings facilitate the dispersion ofwater-immiscible liquids into water and water-containing media, such aswet soil. Droplets encapsulated in this manner are particularly usefulin agriculture, where water from irrigation, rain, and water sprays isfrequently present. A variety of processes for producing such capsulesis known.

Interfacial polymerization is one type of process for producing thesecapsules. Typically, interfacial polymerization involves preparation oftwo distinct phases. One of the film-forming reactants is dissolved inan aqueous phase and the other reactant is dissolved in a hydrophobicphase. Reaction between the two film-forming reactants occurs at thephase interface when the phases are placed in contact with each other.

A second type of interfacial polymerization process is disclosed in U.S.Pat. Nos. 4,046,741 (Scher, Sept. 6, 1977) and in copending applicationSer. No. 922,473, now U.S. Pat. No. 4,285,720. Applicant's processdiffers from typical interfacial polymerization processes in that one ofthe film-forming reactants is formed in situ. Material to beencapsulated and at least one polyisocyanate are present in an organicphase. A surfactant and a protective colloid are present in an aqueousphase. After dispersion of the organic phase into the aqueous phase andheating, the isocyanate monomers react with water at the phase interfaceto form an amine. This amine then reacts with remaining isocyanatemonomers to form a polyureamicrocapsule wall which encapsulates the"material to be encapsulated." The product of this process is aformulation and includes the microcapsules dispersed in water.

The purpose of the protective colloid which is present in the aqueousphase of Applicant's process is to prevent recombination of particlesduring the wall formation step. Among the protective colloids previouslydisclosed are polyacrylates, methylcellulose, polyvinyl alcohol,polyacrylamide and poly(methylvinyl ether/maleic anhyride).

Pesticide loading refers to the amount of pesticide present in a givenquantity of formulation. The maximum pesticide loading which can beachieved using any one of the previously disclosed protective colloidsis about 2.5 pounds (1b) of pesticide/gallon (gal) of formulation. Abovethat level, recombination, foaming or gellation may become a problem.

SUMMARY OF THE INVENTION

It has now been discovered that a graft copolymer of polyvinyl alcoholand methyl vinyl ether/maleic acid has properties as a protectivecolloid for Applicant's microencapsulation system far superior to anyprotective colloids previously described. This graft protective colloidhas excellent protective action. No recombination of particles duringformation of the microcapsule wall occurred even at a pesticide loadingof 4 lb of pesticide/gal of microcapsule formulation. This is about 1.5lb/gal (a 60% increase) greater than anything previously achieved. Inaddition, foaming due to escaping carbon dioxide gas can easily becontrolled and gellation was not a problem.

A graft copolymer of polyvinyl alcohol and poly (methylvinylether/maleic anhydride) is known in the prior art. For example, U.S.Pat. No. 2,609,350 (Spatt, Dec. 21, 1946) discloses such a copolymer foruse as an impregnating composition to impart a permanent finish totextiles.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to use of a graft copolymer of polyvinyl alcoholand methylvinyl ether/maleic acid (hydrolyzed methylvinyl ether/maleicanhydride) as a protective colloid in a process for formingmicrocapsules by interfacial polymerization. A process in which thepresent invention is particularly useful is described in copendingapplication Ser. No. 922,473 and may be briefly summarized as follows:

Material to be encapsulated and at least one polyisocyanate are presentin an organic phase. Examples of pesticides suitable as material to beencapsulated include the following:

HERBICIDES

S-ethyl-N-cyclohexyl-N-ethylthiocarbamate (cycloate)

S-ethyl hexahydro-1H-azepine-1-carbothioate (molinate)

S-2,3-dichloroallyl di-isopropylthiocarbamate (di-allate)

S-2,3,3-trichloroallyl di-isopropylthiocarbamate (tri-allate)

S-ethyl dipropylthiocarbamate (EPTO)

S-4-chlorobenzyl diethylthiocarbamate (benthiocarb)

S-ethyl diisobutylthiocarbamate (butylate)

S-benzyl di-sec-butylthiocarbamate

S-propyl dipropylthiocarbamate (vernolate)

S-propyl butylethylthiocarbamate (pebulate)

N,N-diallylchloroacetamide (allidochlor)

α-chloro-6'-ethyl-N-(2-methoxy-1-methylethyl)-acetanilide (metolachlor)

N-butoxymethyl-α-chloro-2',6'-diethylacetanilide (butachlor)

S-(O,O-diisopropyl phosphorodithioate) ester ofN-(2-mercaptoethyl)benzenesulfonamide (bensulide)

N-benzyl-N-isopropyltrimethylacetamide (butam)

2-chloroallyl diethyldithiocarbamate (CDEC)

2-sec-butyl-4,6-dinitrophenol (dinoseb)

2,6-dinitro-N,N-dipropylcumidine (isopropalin)

N-(cyclopropylmethyl)-α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine(profluralin)

2-(1,2-dimethylpropylamino)-4-ethylamino-6-methylthio-1,3,5-triazine(dimethametryn)

2-ethyl-5-methyl-5-(2-methylbenzyloxy)-1,3-dioxane

INSECTICIDES

S-tert-butylthiomethyl O,O-diethyl phosphorodithioate (terbufos)

O,O-diethyl-O-4-methylsulphinylphenyl phosphorothioate (fensulfothion)

O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate(diazinon)

O,O-diethyl S-2-ethylthioethyl phosphorodithioate (disulfoton)

S-chloromethyl O,O-diethyl phosphorodithioate (chlormephos)

O-ethyl S,S-dipropyl phosphorodithioate (ethoprophos)

O,O-diethyl S-ethylthiomethyl phosphorodithioate (phorate)

O-(4-bromo-2-chlorophenyl) O-ethyl S-propyl phosphorodithioate(prophenofos)

S-1,2-di(ethoxycarbonyl)ethyl O,O-dimethyl phosphorodithioate(malathion)

O,O,O',O'-tetraethyl S,S'-methylene di(phosphorodithioate) (ethion)

O-(4-bromo-2,5-dichlorophenyl) O,O-diethyl phosphorothioate(bromophos-ethyl)

S-4-chlorophenylthiomethyl O,O-diethyl phosphorodithioate(carbophenothion)

2-chloro-1-(2,4-dichlorophenyl)vinyl diethyl phosphate(chlorphenvinphos)

O-2,5-dichloro-4-(methylthio)phenyl O,O-diethyl phosphorodithioate(chlorthiophos)

O-4-cyanophenyl O,O-dimethyl phosphorothioate (cyanophos)

O,O-dimethyl O-2-methylthioethyl phosphorothioate (demephion)

O,O-diethyl O-2-ethylthioethyl phosphorothioate (demeton)

O-2,4-dichlorophenyl O,O-diethyl phosphorothioate (dichlorofenthion)

O-2,4-dichlorophenyl O-ethyl phenylphosphonothioate (EPBP)

O,O-diethyl O-5-phenylixoxazol-3-yl phosphorothioate (isoxathion)

1,3-di(methoxycarbonyl)-1-propen-2-yl dimethyl phosphate

S,S'-(1,4-dioxane-2,3-diyl) O,O,O'O'-tetraethyl di(phosphorodithioate)(dioxathion)

O,O-dimethyl-O-4-nitro-m-tolyl phosphorothioate (fenitrothion)

O,O-dimethyl O-4-methylthio-m-tolyl phosphorothioate (fenthion)

O-(5-chloro-1-isopropyl-1,2,4-triazol-3-yl) O,O-diethyl phosphorothioate(isazophos)

S-2-isopropylthioethyl O,O-dimethyl phosphorodithioate (isothioate)

4-(methylthio)phenyl dipropyl phosphate (propaphos)

1,2-dibromo-2,2-dichloroethyl dimethyl phosphate (naled)

O,O-diethyl α-cyanobenzylideneamino-oxyphosphonothioate (phoxim)

O,O-diethyl O-4-nitrophenyl phosphorothioate (parathion)

O-2-diethylamino-6-methylpyrimidin-4-yl O,O-diethyl phosphorothioate(pirimiphos-ethyl)

O-2-diethylamino-6-methylpyrimidin-4-yl O,O-dimethyl phosphorothioate(pirimiphos-methyl)

(E)-O-2-isopropoxycarbonyl-1-methylvinyl O-methylethylphosphoramidothioate (propetamphos)

O,O,O',O'-tetraethyldithiopyrophosphate (sulfotep)

O,O,O',O'-tetramethyl O,O'-thiodi-p-phenylene diphosphorothioate(temephos)

S-2-ethylthioethyl O,O-dimethyl phosphorodithioate (thiometon)

O,O-diethyl O-1-phenyl-1,2,4-triazol-3-yl phosphorothioate (triazophos)

O-ethyl O-2,4,5-trichlorophenyl ethylphosphonothioate (trichloronate)

(±)-3-allyl-2-methyl-4-oxocyclopent-2-enyl (±)-cis,trans-chrysanthemate(allethrin)

(±)-3-allyl-2-methyl-4-oxocyclopent-2-enyl (±)-trans-chrysanthemate(bioallethrin)

3-phenoxybenzyl (±)-cis,trans-chrysanthemate (phenothrin) pyrethrins

2-(2-butoxyethoxy)ethyl thiocyanate

isobornyl thiocyanoacetate (terpinyl thiocyanoacetate)

carbon disulfide

2-(4-tert-butylphenoxy)cyclohexyl prop-2-ynyl sulphite (propargite)

4,6-dinitro-6-octylphenyl crotonates (dinocap)

ethyl 4,4'-dichlorobenzilate (chlorobenzilate)

DEFOLIANTS

S,S,S-tributyl phosphorothioate

tributyl phosphorotrithioite (merphos)

FUNGICIDES

copper naphthenates

5-ethoxy-3-trichloromethyl-1,2,4-thiadiazole (etridiazole)

O-ethyl S,S-diphenyl phosphorodithioate (edifenphos)

INSECT REPELLENTS

6-butoxycarbonyl-2,3-dihydro-2,2-dimethylpyran-4-one (butopyronoxyl)

N,N-diethyl-m-toluamide (deet)

dibutyl phthalate

dibutyl succinate

1,5a,6,9,9a,9b-hexahydro-4a(4H)-dibenzofurancarboxaldehyde

dipropyl pyridine-2,5-dicarboxylate

The polyisocyanate, which is also present in the organic phase, reactswith water to form an amine. This amine then reacts with additionalisocyanate monomers to form a polyurea capsule wall. Suitablepolyisocyanates include aromatic diisocyanate, aliphatic diisocyanate,high molecular weight linear aliphatic diisocyanates, isocyanateprepolymers and combinations thereof. It is important, for purposes ofthe present invention, that the capsular wall be formed frompolyisocyanates or a combination of polyisocyanates with other monomers.

A surfactant and a protective colloid are present in an aqueous phase.The purpose of the surfactant is to lower the surface tension of thefluid interface when the aqueous phase is brought into contact with theorganic phase. Examples of suitable surfactants include sodium isopropylnaphthalene sulfonate, polyoxyethylenesorbitol oleate laurate,ethoxylated nonylphenols and polyethylene glycol ethers of linearalcohols.

The protective colloid stabilizes the system against aggregation,flocculation and coalescense when the organic phase is dispersed intothe aqueous phase. The present invention relates to an improvedprotective colloid for use in an interfacial polymerization system suchas the one being described. Prior art protective colloids includepolyacrylates, methyl cellulose, polyvinyl alcohol, polyacrylamide andpoly(methylvinyl ether/maleic anhydride).

To form the microcapsule wall, the organic phase is dispersed into theaqueous phase. Reaction of the polyisocyanate with water to form anamine and subsequent reaction of this amine with additional isocyanateto form a polyurea wall is accomplished by appropriate adjustment oftemperature and pH.

The present invention comprises the use of an improved protectivecolloid in the process described. This improved protective colloid is agraft copolymer of polyvinyl alcohol and hydrolyzed methylvinylether/maleic anhydride.

The optimum weight ratio of hydrolyzed methylvinyl ether/maleicanhydride (Gantrez® AN119 (MW=250,000)) to polyvinyl alcohol (Vinol® 205(MW=10,000)) for the preparation of the graft protective colloid is30/1. This represents a molecular ratio of 1/1. Weight ratios about 30/1are optimum. Higher ratios are not as effective in preventingrecombination and lower ratios may cause foam problems. However, weightratios within the broad range of 300:1 hydrolyzed methylvinylether/maleic anhydride:polyvinyl alcohol to 10:1 hydrolyzed methylvinylether/maleic anhydride:polyvinyl alcohol may be used depending on otherreaction conditions.

The graft protective colloid may be prepared by varying methods asillustrated by the following examples.

EXAMPLE I

Twenty-nine grams (29 g) of Gantrez® AN119 (General Aniline and FilmCorp.) were dispersed in 266.0 g of water at room temperature (25° C.).Five g of a 20% aqueous solution of Vinol® (Air Products and Chemicals,Inc.) were blended in. The slurry was warmed to 70° C. and stirring wasmaintained for 2 hours. The resulting solution was hazy and viscous.

EXAMPLE II

Seventy-nine and two-tenths g of Gantrez® AN119 and 0.88 g of Vinol® 205were dispersed in 320 g of water at 40° C. The slurry was warmed up to70° C. with stirring. These conditions were maintained for 2 hours,resulting in hazy viscous fluid.

EXAMPLE III

Thirty-eight g of Gantrez® AN119 and 1.9 g of Vinol® 205 were dispersedin 360 g of water at room temperature. The slurry was warmed to 95° C.and stirring at this temperature was maintained for 2 hours, resultingin formation of a hazy, viscous fluid.

EXAMPLE IV

Eighteen and two-tenths g of Gantrez® AN119 and 1.82 g of Vinol® 205were dispersed in water at room temperature. Stirring was maintained for24 hours, resulting in the formation of a hazy fluid.

Physically, there is evidence for the formation of a Vinol® 205/Gantrez®An119 graft protective colloid by the methods described. The resultingsolution is turbid whereas the individual solutions of Vinol® 205 andGantrez® AN119 and mixtures thereof are clear.

Use of Protective Colloid

The graft protective colloid is initially present in the aqueous phaseof an interfacially polymerizable system. Its purpose is to prevent therecombination of particles during the wall formation step. The followingare examples of how the graft protective colloid is used:

EXAMPLE V-VIII

Preparation of the organic phase, aqueous phase, and the microcapsulewall was the same in each of these examples.

An organic phase, comprising 340.4 g of S-ethylN,N-diisobutylthiolcarbamate (material to be encapsulated), 15.2 g ofpolymethylenepolyphenyl isocyanate and 12.5 g of toluene diisocyanatewas prepared. An aqueous phase, comprising 56.2 g of a 10% colloid graftsolution, 4.2 g of a 20% aqueous solution of Tergitol® 15-S-7 (UnionCarbide) and 220.6 g of water was prepared. The organic phase wasdispersed into the aqueous phase and heated to form the microcapsulewall.

The ratio of Gantrez® AN119:Vinol® 205 varied for each example. Thefollowing table shows the ratios used and the observed results.

    ______________________________________                                                 Ratio Gantrez ®                                                           AN119:Vinol ® 205                                                Example No.                                                                            In Graft Polymer                                                                              Results                                              ______________________________________                                        V        3.33:1          no recombination                                     VI         10:1          no recombination                                     VII      28.5:1          no recombination                                     VIII      100:1          recombination of par-                                                         ticles after heating                                                          at 50° C. for 10 min-                                                  utes                                                 ______________________________________                                    

The results shown for Examples IV-VIII, in particular, may be contrastedwith the following example in which a simple polymer mixture was used inplace of a graft protective colloid.

EXAMPLE IX

An organic phase was prepared as in the previous examples. An aqueousphase comprising 50.6 g of a 10% aqueous Gantrez® AN119 solution, 2.8 gof a 20% aqueous Vinol® 205 solution (ratio of Gantrex® AN119:Vinol® 205is 10:1), 4.2 g of a 20% aqueous Tergitol® 15-S-7 solution and 223.4 gof water was prepared. The organic phase was dispersed into the aqueousphase and heated to form the microcapsule wall. Severe recombination ofparticles occurred on reaching 50° C.

What is claimed is:
 1. In an interfacial polymerization processcharacterized by the steps of:(a) combining a material to beencapsulated and at least one polyisocyanate in an organic phase; (b)incorporating a surfactant and a protective colloid in an aqueous phase;(c) dispersing the organic phase into the aqueous phase; and (d) forminga polyurea-microcapsule wall at the phase interface, the improvementwhich comprises,using a protective colloid comprising a graft copolymerof polyvinyl alcohol and methyl vinyl ether/maleic acid.
 2. In aninterfacial polymerization process as defined in claim 1, furthercharacterized by forming the polyurea microcapsule wall frompolyisocyanates or a combination of polyisocyanates and other monomers,the improvement which comprises using a protective colloid comprising agraft copolymer of polyvinyl alcohol and methyl vinyl ether/maleic acid.3. In an interfacial polymerization process as defined in claim 1,wherein the improvement further comprises using the protective colloidin a weight ratio in the range of about 1:10 to about 1:300 polyvinylalcohol to methyl vinyl ether/maleic acid.